Machines such as loaders are used generally to transfer bulk material from a stock pile onto transport machines such as trucks or railroad cars. In such machine loading applications, it typically is desirable that the transport machines are loaded to, but not over, their maximum rated capacity. Underloading of a machine causes inefficiency in the material hauling cycle and under-utilization of such transport machines. Overloading causes additional maintenance cost and extra wear on tires and suspension systems of the machine. Furthermore, the overloaded material may need to be unloaded to decrease load weight, thus causing additional expense. Therefore, accurate payload measurement is desirable.
Payload measurement is also desirable as a method of determining operation productivity. For example, the ability to accumulate the weight of the material loaded during a single shift, during a twenty-four hour period, or during any other time period may be valuable to an operations manager.
Payload measurement systems have been developed which utilize sensed lift cylinder pressures which enable the system to be calibrated using known weights and then to determine payload weight during the operation of the machine. This measurement method is dependent on the pressure to weight ratio remaining consistent between the time the machine is calibrated and the time the machine is measuring an unknown load. In addition, such systems assume the pressure to weight ratio remains consistent over a wide temperature range. It is known to adjust a measurement system for changes in ambient temperature; in addition, it is generally known to compensate a measured payload for changes in the actuating fluid temperature. Such systems typically scale the measured payload weight with an absolute coefficient. However, using an absolute number does not take into account changes in the relative weight of the load.
The present invention is directed to overcoming one or more of the problems set forth above.